Steel production method and apparatus

ABSTRACT

A metallurgical vessel having an energy source and in which molten metal is contained for processing. A tuyere system is provided below the level of molten metal to permit the injection of gases, fluxes, ores, alloying additions and other materials to convert the molten metal to steel.

United States Patent Schempp et al.

[451 Sept. 16, 1975 STEEL PRODUCTION METHOD AND APPARATUS I [75] Inventors: Eberhard G. Schempp; Jai K.

Pearce; David L. Schroeder, all Of Pittsburgh, Pa.

[73] Assignee: Pennsylvania Engineering Corporation, Pittsburgh, Pa.

[22] Filed: Mar. 27, 1972 [21] Appl. NO.: 238,338

[52] US. Cl 266/35; 13/10 [51] Int. Cl. C2lc 7/00 [58] Field of Search 75/59, 60; 13/10, 26, 27, 13/35, 1, 2, 34; 266/34 A, 34 PP, 34 V, 35, 36 P, 41

[56] References Cited UNITED STATES PATENTS 707,776 8/1902 Heroult 266/35 1,031,257 7/1912 Greene 13/26 1,070,337 8/1913 Greene 13/26 1,078,619 11/1913 Greene 13/27 1,763,248 6/1930 Moore 266/35 2,528,571 ll/l9 50 Babcock et al. 13/10 3,246,889 4/1966 Sieckman et al. 266/34 V 3,330,645 7/1967 De Moustier et al. 75/60 3,382,912 5/1968 Philbrick 266/34 V 3,443,806 5/1969 Galey et al.. 266/34 A 3,501,290 3/1970 Finkl et a1 266/34 V 3,706,549 12/1972 Knuppel et al. 75/60 FOREIGN PATENTS OR APPLICATIONS 2,076 5/1879 United Kingdom 266/36 P 585,737 12/1959 Belgium 266/35 Primary ExaminerGerald A. Dost Attorney, Agent, or FirmFred Wiviott; Ralph G.

' Hohenfeldt [5 7 ABSTRACT A metallurgical vessel having an energy source and in which molten metal is contained for processing. A tuyere system is provided below the level of molten metal to permit the injection of gases, fluxes, ores, alloying additions and other materials to convert the molten metal tO steel.

5 Claims, 5 Drawing Figures MTENTEU SEP 1 e 1975 NET 1 OF 3 FIG-l FIGZ PATENTED SW5 3, 9 05 589 sum 2 BF 3 Ila 1 STEEL PRODUCTION lVIETHOD AND APPARATUS BACKGROUND OF THE INVENTION In the production of steel, it is common practice to perform distinct process steps either in the same vessel or to perform a first portion of the process in one vessel and second portion in a separate vessel. For example, it is common in the use of electric arc furnaces for the processing of steel to employ separate slags for oxidation and refining. Initially, a melt down period is pro vided to form a molten bath. During oxidation, silicon, manganese, carbon and other materials in the melt are oxidized. The oxygen for this purpose may be provided in a number of ways, such as by an oxygen lance, the furnace atmosphere, the calcination of limestone or ox ides from alloying elements and/or ores which may be added to the furnace charge. During the oxidation period, the melt is covered by an oxidizing slag which typically includes large percentages of oxides of ion, aluminum, magnesium, manganese and phosphorous. At the end of the oxidizing period, it is generally the practice to deslag the melt by cutting off the power to the electrodes which are then raised, tilting the furnace and racking off the oxidizing slag through a slag door. The furnace would then be charged with materials such as burnt lime, fluorspar, silicon, sand and powdered coke to form a reducing slag which would be maintained during the reducing period. The disadvantages of the multi-slag electric arc furnace steel making process is that it is relatively lengthy and results in a high iron loss as the result of the deslagging operation.

It is a common practice in electric arc steel making to preheat scrap before charging so as to reduce the duration of the meltdown period. This has not been wholly satisfactory because it involves additional handling and equipment.

There are also a number of metallurgical vessels presently employed which perform an inactive function, such as metal storage or are limited in the functions that can be performed, such as induction melting furnaces.

SUMMARY OF THE INVENTION An object of the invention is to provide a metallurgical apparatus capable of performing its intended functions more rapidly than conventional apparatus of the same type.

A further object of the invention is to provide metallurgical apparatus capable of greater flexibility than conventional apparatus.

Another object of the invention is to provide metallurgical apparatus which is more economical to operate than conventional apparatus.

A still further object of the invention is to provide a more efficient and economical method of processing molten metal.

These and other objects and advantages of the instant invention will become more apparent from the detailed description thereof taken with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 schematically illustratesan electric arc furnace incorporating the instant invention;

FIG. 2 shows the tuyere system of the furnace illus trated in FIG. 1 in greater detail;

FIG. 3 schematically illustrates an induction furnace incorporating the instant invention;

FIG. 4 schematically illustrates a holding furnace incorporating the instant invention; and

FIG. 5 schematically illustrates means for controlling the delivery of gases and other materials to the vessels shown in FIGS. 1-4.

DESCRIPTION OF THE PREFERRED ENIBODIMENT FIG. 1 shows an electric arc furnace l0 incorporating the tuyere system 1 1 according to the instant invention. The furnace 10 includes a metallic shell 12 and a refractory lining 13. In the case of a basic furnace, the refractory lining would be composed of any suitable basic material, such as magnesite or high alumina brick. The furnace 10 generally includes a cylindrical body portion 14, an arched roof l5 and a dished hearth 16. A smoke hood, not shown, may be provided for venting gases and conducting the same to a gas cleaning apparatus (not shown).

One or more electrodes 17 extend through openings 18 formed in roof 16 for providing the heat energy input to the furnace, As those skilled in the art will appreciate, the number of electrodes will be determined by whether alternating or direct current energy is employed and whether the alternating current systems are single phases or polyphase. The electrodes 17 are supported by a conventional support assembly (not shown) for moving the electrodes vertically relative to the hearth 16 and which generally include conventional electrode clamps (not shown) for conducting electrical energy to the electrodes 17.

Electric arc furnaces of the type illustrated are typically mounted for pivotal movement such as by means of the rocker 20 so that the furnace 10 may be pivoted in a first direction to discharge the molten metal bath 21 from a pouring spout 22 and in the opposite direction to discharge slag through a deslagging door 24 at the opposite side of the furnace 10. The roof 15 of arc furnaces of the type illustrated in FIG. 1 are typically constructed and arranged to be lifted vertically by means of lugs 25 and swung laterally away from the furnace body to permit charging. At the same time, the electrodes 17 are raised by the mechanism 19 and similarly swung away from the furnace 10.

As shown more specifically in FIG. 2, the furnace 10 is also provided with a tuyere system 1 l which may include a monolithic refractory member 26 formed, for example, from any suitable cast, rammed or brick refractory material. The refractory member 26 is suitably received within an opening 27 formed in the hearth l6 and which is displaced off-center and toward the slag door 24 as seen in FIG. 1. Referring again to FIG. 2, a metallic backup plate 28 may be suitably secured to the under side of refractory member 26 and may be simi larly received within an opening formed in the metallic outer shell 12. A plurality of spaced-apart tuyere passages 29 are formed in refractory member 26 and plate 28 for receiving a plurality of metallic tuyere assemblies. Each tuyere assembly includes a pair of concentricly spaced tuyere pipes 31 and 32 which are respectively coupled to manifold pipes 33 and 34. More specifically, the tuyere pipes 31 extend from manifold 33 and concentrically through the outer pipe 32 for conducting oxygen and entrained powdered material into the vessel. Each of the outer pipes 32 are connected to and supported by a union 35 through which the pipes 31 also pass. The unions in turn are connected by pipes 36 to the manifold pipe 34 for conducting a hydrocarbon fluid to the outer tuyere 32.

In operation of the furnace 10, the roof and electrodes 17 will normally be swung away from the body of the furnace andthe furnace charged, usually with scrap. The roof 15 is then repositioned and the electrodes 18 are energized to commence the meltdown. Initially, a molten bath begins to form in the hearth 16 at which time the blowing of the gases or other materials through the tuyere system 11 may commence. This will usually take the form of oxygen or an oxygen containing gas provided through the inner pipes 31 while a hydrocarbon fluid, such as propane gas, is injected through the outer tuyere pipes 32 for the purpose of prolonging refractory life. When an inert gas, such as argon or nitrogen is injected into the bath 22, for reasons which will be described more fully below, the propane will not be required so that the same inert gas will normally be injected through both tuyere pipes 31 and 32.

Alternately, the blowing of oxygen and hydrocarbon gases may commence prior to or during the meltdown period whereby the oxidation of the hydrocarbon acts to preheat the scrap and thereby shorten the meltdown period.

The tuyere system 11 may be offset with respect to the center of the hearth 16 and one the side closest to the slag door 24 so that the tuyere pipes 31 and 32 will remain below the level of the bath 22 should it become necessary to tilt the vessel for deslagging.

This permits the continued injection of gases and other materials through tuyeres 30 during a deslagging operation so that the process need not be interrupted. Further, powdered material for a second slag may then be blown into the vessel system 1 1. As an alternate, the tuyeresmay be located so that they would be above the bath level during deslagging and/or pouring to prolong tuyere life. For example, the tuyeres could be located near the rotational axis of the vessel for the latter purpose.

Because an oxidizing gas is introduced into the bath during the oxidation period, the oxidation of elements such as phosphorous, silicon, mangenese and carbon may proceed rapidly. The use of oxygen further promotes a vigorous boiling action in the bath 22 to pro mote the desired reactions as well as mixing to promote homogeneity. Desulphurization may be accomplished by the injection of powdered lime in the gas stream injected through inner tuyere pipe 31. Further, if stainless or silicon steels are to be produced, a mixture of oxygen and an inert gas such as argon may be fed into the bath through the tuyere system 11. The argon reduces the partial pressure of CO in the bath so that a greater reduction in the carbon level may be obtained. After the bath 22 has been decarborized to the desired degree, the bath 22 may be reduced by the addition of suitable powdered materials such as lime, limestone, fluorspar or burnt lime and entrained in the gas stream through the tuyere system 11. Thus, even in the production of low carbon steels, a separate oxidizing slag and the subsequent deslagging step prior to reduction is not required. This not only shortens the process time but reduces iron loss from the melt. Further, final adjustments can also be made by the introduction of the requisite materials through the tuyere system 11. For

example, if the carbon level-is too low, a powdered car bonaceous material or a hydrocarbon gas can be introduced into the melt along with an inert gas such as argon or nitrogen. If a hydrocarbon fluid is introduced for recarburization, normally through the inner tuyere pipe 31, an inert gas such as argon or nitrogen will be introduced through the other tuyere pipe 32. On the other hand, if a reduction in the carbon level is required, oxygen would be introduced through the inner tuyere pipe 31 during this period and a hydrocarbon gas introduced through outer tuyere pipe 32. Also, the bath can be efficiently purged of hydrogen or nitrogen by the introduction of an inert gas such as argon. Additionally, bath temperature can be closely controlled either by the introduction of oxygen to increase temperature, or coolants such as lime or iron ore entrained in an inert carrier gas, such as argon. In this manner, the use of the tuyere system 11 in the arc furnace 10 substantially reduces the operating time required because the various chemical reactions are facilitated by the introduction of oxidizing and reducing materials through the bath rather than relying on the interaction between the bath and the slag. The desired chemical reactions are also promoted as a result of the mixing action caused by the introduction of gases through tuyere system l 1.

FIG. 3 schematically illustrates an induction furnace 60. In general terms, furnace includes an outer metallic shell 61 and a refractory lining 62. A generally annular induction coil 63 may be embedded in the lining 62 and in a generally surrounding relation to the inner chamber 64 of furnace 60. A tuyere assembly 11b is disposed in the lower end of the furnace 60 and may be identical to that shown in FIG. 2 and accordingly will not be discussed in detail for the sake of brevity.

As those skilled in the art will appreciate, when the coil 63 is energized with an alternating current, secondary currents are induced and the metal disposed within chamber 64. These secondary currents are converted into heat by the electrical resistance of the charge and in addition a vigorous stirring action is produced. Induction furnaces are generally employed to provide relatively homogeneous melts made possible by this stirring action. Generally, oxidation and reduction of metal are not carried out in induction furnaces. By the use of the tuyere system 11b, however, oxidation, reduction and finishing as well as slag control can be effectively carried out in the induction furnace 60 by the introduction of oxygen, inert gases, hydrocarbon gases, and powdered materials such as lime, limestone, burnt lime, fluorspar or iron ore below the surface of the melt in the manner discussed above in relation to furnace FIG. 4 illustrates a holding furnace which includes a metallic shell 71 and a refractory lining 72. Furnace 70 may be provided with a hot metal receiving spout 73 and a pouring spout 74. The furnace 70 normally receives hot metal 76 from a melting furnace, not shown, through pouring spout 73. The metal 76 is retained in furnace 70 until needed at which time the furnace is pivoted by means (not shown) which tilts the furnace about an axis normal to the plane of FIG. 4 for discharging metal 76 through pouring spout 76 and into a mold or tundish, for example. In order to maintain the melt 76 at the desired temperature, a heat source, such as graphite rod 75 may be provided. As those skilled in the art will appreciate, the rod 75 will be connected to and which heat is radi- Normally, metallurgical reaction s 'are jr'iot"performed in the holding furnace 70. The additionof a tuyere 'systern 110 into the bottom of the furnace 70-,- however,

permits the latter to be employed for the ox-idation,-re-' fining or finishing-of metal melts by the introduction of oxygen, carbonaceous materials, lime, burnt lime, limestone, fluorspar, etc., and inert gases as discussed hereinabove. The tuyere system llc may be'identical to that shown in FIG. 2 and will not be discussed in detail for the sake of brevity.

The method for controlling the delivery of gases and powdered materials to the various vessels 10, 50, 60 or 70 may be substantially identical. Accordingly, such apparatus will be discussed solely with respect to vessel for the sake of brevity.

When a heat is in process in vessel 10, various gases, primarily oxygen, are delivered to the bath22 through tuyere system 1 1 and powdered materials such as lime, burnt lime, limestone, iron oxide, desulfurizing agents, and fluorspar may be entrained from pressure vessels 80 and 81 in,the gas stream and injected in the melt in accordance with the process requirements. Only two pressure vessels 80 and 81 for containing powdered material are shown but it will be understood that there will be as many pressure vessels as there are types of powdered materials which are to be injected into the bath 22 within vessel 10.

Powdered materials may be delivered consecutively or concurrently to tuyere system 11 through header pipes 82 and 83 which are connected to pipe 36 for furnishing the powdered materials. The powdered materials are, of course, entrained in whatever gas or gases that are being blown into vessel 10 at a particular time. It is necessary to mix the powdered material from a vessel such as 80 with entraining gas in definite proportion. For this purpose, the bottom of a vessel 81, for instance, is provided with a mixing device 84, the details of which are not shown, but are well known in the art. For example, the device 84 may be of the type which withdraws powdered material from vessel 80 and injects it into the gas stream. The device 84 may be operated by motive means 85 with a controller 86. The controller may be responsive to input signals from any suitable control source, as symbolized by the short arrowhead line 87. Mixing device 84 and 84 are associated with each pressure vessel 80 and 81, respectively, and each is connected to as many sources of gas as might be blown in a particular installation. Thus, from a source of oxygen which is labeled 0 oxygen may be delivered from a header 88 through a branch pipe 89, a remotely controllable valve 90 and a pipe 91 to mixing device 84. An arrow, such as 62, symbolizes that valve 60 receives control signals for throttling or turning off the flow of oxygen to mixing device 84. These control signals may be provided from any suitable control equipment (not shown).

Other control valves may also be interposed between mixing device 84 and the sources of other gases. However, only the aforementioned controllable valve 90, connected between an air source and mixing device 84, is shown for the sake of brevity. For example, there may be additional valves interposed between air, argon and nitrogen and gas sources which are respectively marked AIR, Ar and N The other pressure vessels LII such as 80, containing powdered materials.may also be supplied with these various gases through suitable pipes and valves, not shown.

The various gases may also-be fed selectively into vessel 10 directly without entraining solid material if desired, The oxygen line, for ihstance connects through remotely controllable'valve 93 to gas header 88 which feeds through remotely controllable valve 94 to input pipe 36 and to tuyere system 11 at the bottom of vessel 10. Remote valves 95 and 96 for preventing reverse flow are also provided and there are also several valves 98-101 for variously directing and regulating gas flow. Similarly, remote controllable valve, 102 and directional regulating valves 103-106 are provided to regulate and control the flow of various gases to the input pipe 33 of the second tuyere system IL-Hydrocarbon gas may be provided to pipe 33 through valve 102 and 107. Extending from each of the remote controlled valves is an arrow which symbolizes, as in re spect to the previously discusses valves, that they are subject to control.

The use of the tuyere system in the metallurgical .vessels 10, 50, 60 or according to the invention, permits the more accurate performance of the desired metallurgical processed and economizes in fuel and electrical energy. Further, the stirring action of the introduction of gasthrough the bath'promotes chemical reactions and a more homogeneous metal. This greater facility'of chemical reactions and the heat generated as a result of the oxidation promoted by the introduction of oxygen, substantially shortens the required treatment periods. In addition, the use of the tuyere system 11 permits the performance of metallurgical processing in vessels not heretofore employed for this purpose.

While only a few embodiments of the invention have been illustrated and described, it is not intended to be limited thereby but only by the scope of the appended claims.

We claim:

1. Apparatus for treating ferrous metal including,

a refractory lined vessel for receiving a quantity of said metal, said vessel having side walls, a removable cover having apertures formed therein and a shallow bottom constructed and arranged to receive molten metal, a plurality of tuyere means extending through said refractory lining and including a first tuyere pipe and a second tuyere pipe spaced from and surrounding said first tuyere pipe, each of said tuyere pipes having a discharge end adjacent the bottom of said vessel and opening into said vessel beneath the level of metal disposed therein for injecting process gases beneath said molten metal,

a plurality of fluid sources,

the outer ends of said tuyere pipes being disposed on the exterior of said vessel and means on the exterior portions of each of said tuyere pipes for connection to individual ones of said fluid sources,

means for selectively connecting predetermined ones of said fluid sources to said first and second tuyere P p a plurality of electrodes extending into said vessel, and means for energizing said electrode means for heating said molten metal by the creation of an electrical discharge therefrom,

means for positioning said electrodes in said apertures and for moving said electrodes in a generally 7 vertical direction toward and away from said hearth to position said electrodes adjacent the molten metal contained in said vessel, means for rocking said vessel about a substantially horizontal axis,

a molten metal discharge opening formed in said refractory lining and on one side of a plane containing the pivotal axis of said vessel for discharging molten metal from said vessel when the latter is pivoted about said axis,

a slag discharge opening formed in said refractory lining and disposed on the other side of said plane so that molten metal may be poured from said vessel when it' is pivoted toward said one side and slag removed when it is pivoted toward said other side,

the open inner ends of each of said tuyere pipes being disposed on said other side of said plane whereby the discharge ends of all of said tuyere pipes remain below the level of molten metal when said vessel is tilted toward said other side for slag removal and when said vessel is in an untilted position, and said discharge ends of all of said tuyere pipes being above the level of molten metal when said vessel is tilted toward said one side to discharge molten metal from said molten metal discharge opening.

2. The apparatus set forth in claim 1 wherein a first one of said fluid sources is oxygen and a second one of said fluid sources if a hydrocarbon shielding fluid, means for respectively coupling said first and second fluid sources to said first and second tuyere pipes,

means for containing powdered material, and means for selectively entraining said powdered material into the fluid stream coupled to said first tuyere pipe.

3. Apparatus for treating ferrous metal including,

a refractory lined vessel having side walls and a bottom constructed and arranged to receive a quantity of molten metal,

a tuyere including a first tuyere pipe and a second tuyere pipe surrounding said first tuyere pipe and spaced therefrom, each of said tuyere pipes, extending entirely through said refractory lining and having discharge ends opening into said vessel and located adjacent the bottom of said vessel and beneath the level ofmolten metal when a quantity of the latter is disposed therein.

heating means disposed within said vessel for heating said molten metal,

means for rocking said vessel about a substantially horizontal axis,

and a molten metal discharge opening formed in said refractory lining and one side of a plane containing the pivotal axis of said vessel for discharging molten metal from said vessel when the latter is pivoted about said axis,

a slag discharge opening formed in said refractory lining and disposed on the other side of said plane so that molten metal may be poured from said vessel when it is pivoted toward said one side and slag removed when it is pivoted toward said other side,

the inner ends of said tuyere pipes being disposed on said other side of said plane whereby their discharge ends remain below the level of molten metal when said vessel is tilted toward said other side for slag removal and when said vessel is in an untilted position, and said inner ends of said tuyere pipes being above the level of molten metal when said vessel is tilted toward said one side to discharge molten metal from said molten metal discharge opening.

4. The apparatus set forth in claim 3 wherein said vessel includes side walls; a shallow hearth and a removable cover, said heating means comprising electrode means, said cover having an opening formed therein for receiving said electrode means, and means for positioning an end of said electrode means relative to the molten metal in said vessel.

5. The apparatus set forth in claim 4 wherein the outer ends of said tuyere pipes being disposed exteriorly of said vessel and means on the exterior portions of each of said tuyere pipes for connection to individual fluid sources.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent: No. 905,, 589 Dated Segtember 16 1975 \lnventor(s) 'E h 'd Schempp et al It is certified thaterror appears in the above-identified patent v n f a nd that said Letters Patent are hereby corrected as shown below:

Claim 1,' Column 6, Line 63, cancel "electrode means" and substitute -electrodes;

Column 7, Line 2, cancel "hearth" and substitute --bottom-.

' Claim 3, Column 8, Line 10, after "and" and before "one" insert Claim 5, Column 8, Line 38, change "being" to "are- Signed and Scaled this A ttes t:

RUTH C. MASON C. MARSH Arrestin 0177 ALL DANN ommissl'nner oj'Parenls and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 589 Dated September 16, 1975 Inventor(s) h d SChempp et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim l, Column 6, Line 63, cancel "electrode means" and substitute -electrodes;

Column 7, Line 2, cancel "hearth" and substitute -bottom--.

Claim 3, Column 8, Line 10, after "and" and before "one" insert Claim 5, Column 8, Line 38, change "being" to are-.

Signed and Scaled this [SEAL] Sixth Day of Aprz'l1976 RUTH C. MASON C. MARSHAL Arresting Officer L DANN ummissiuncr ufParents and Trademarks 

1. Apparatus for treating ferrous metal including, a refractory lined vessel for receiving a quantity of said metal, said vessel having side walls, a removable cover having apertures formed therein and a shallow bottom constructed and arranged to receive molten metal, a plurality of tuyere means extending through said refractory lining and including a first tuyere pipe and a second tuyere pipe spaced from and surrounding said first tuyere pipe, each of said tuyere pipes having a discharge end adjacent the bottom of said vessel and opening into said vessel beneath the level of metal disposed therein for injecting process gases beneath said molten metal, a plurality of fluid sources, the outer ends of said tuyere pipes being disposed on the exterior of said vessel and means on the exterior portions of each of said tuyere pipes for connection to individual ones of said fluid sources, means for selectively connecting predetermined ones of said fluid sources to said first and second tuyere pipes, a plurality of electrodes extending into said vessel, and means for energizing said electrode means for heating said molten metal by the creation of an electrical discharge therefrom, means for positioning said electrodes in said apertures and for moving said electrodes in a generally vertical direction toward and away from said hearth to position said electrodes adjacent the molten metal contained in said vessel, means for rocking said vessel about a substantially horizontal axis, a molten metal discharge opening formed in said refractory lining and on one side of a plane containing the pivotal axis of said vessel for discharging molten metal from said vessel when the latter is pivoted about said axis, a slag discharge opening formed in said refractory lining and disposed on the other side of said plane so that molten metal may be poured from said vessel when it is pivoted toward said one side and slag removed when it is pivoted toward said other side, the open inner ends of each of said tuyere pipes being disposed on said other side of said plane whereby the discharge ends of all of said tuyere pipes remain below the level of molten metal when said vessel is tilted toward said other side for slag removal and when said vessel is in an untilted position, and said discharge ends of all of said tuyere pipes being above the level of molten metal when said vessel is tilted toward said one side to discharge molten metal from said molten metal discharge opening.
 2. The apparatus set forth in claim 1 wherein a first one of said fluid sources is oxygen and a second one of said fluid sources if a hydrocarbon shielding fluid, means for respectively coupling said first and second fluid sources to said first and second tuyere pipes, means for containing powdered material, and means for selectively entraining said powdered material into the fluid stream coupled to said first tuyere pipe.
 3. Apparatus for treating ferrous metal including, a refractory lined vessel having side walls and a bottom constructed and arranged to receive a quantity of molten metal, a tuyere including a first tuyere pipe and a second tuyere pipe surrounding said first tuyere pipe and spaced therefrom, each of said tuyere pipes, extending entirely through said refractory lining and having discharge ends opening into said vessel and located adjacent the bottom of said vessel and beneath the level of molten metal when a quantity of the latter is disposed therein. heating means disposed within said vessel for heating said molten metal, means for rocking said vessel about a substantially horizontal axis, and a molten metal discharge opening formed in said refractory lining and one side of a plane containing the pivotaL axis of said vessel for discharging molten metal from said vessel when the latter is pivoted about said axis, a slag discharge opening formed in said refractory lining and disposed on the other side of said plane so that molten metal may be poured from said vessel when it is pivoted toward said one side and slag removed when it is pivoted toward said other side, the inner ends of said tuyere pipes being disposed on said other side of said plane whereby their discharge ends remain below the level of molten metal when said vessel is tilted toward said other side for slag removal and when said vessel is in an untilted position, and said inner ends of said tuyere pipes being above the level of molten metal when said vessel is tilted toward said one side to discharge molten metal from said molten metal discharge opening.
 4. The apparatus set forth in claim 3 wherein said vessel includes side walls, a shallow hearth and a removable cover, said heating means comprising electrode means, said cover having an opening formed therein for receiving said electrode means, and means for positioning an end of said electrode means relative to the molten metal in said vessel.
 5. The apparatus set forth in claim 4 wherein the outer ends of said tuyere pipes being disposed exteriorly of said vessel and means on the exterior portions of each of said tuyere pipes for connection to individual fluid sources. 